Blow molded article with reverse lip

ABSTRACT

An apparatus and method for blow molding a recessed lip in a molded article. The apparatus includes two plates reciprocally movable toward and away from one another. A center ring member is fixedly and perpendicularly mounted on each plate. A mold half is mounted on each plate and is divided into two sections. One section is located on each side of the center ring member and is reciprocally movable toward and away from the center ring member. A first ring member is affixed to each section in proximity to the center ring member and has a channel. A second ring member is reciprocally movable in the channel and engages the center ring member. The recessed lip is molded between the center ring member, the first ring member and the second ring member.

FIELD OF THE INVENTION

The present invention is directed to blow molding plastic articles, andis specifically directed to a blow molding apparatus and method whichforms a deep recessed or reverse lip in the article.

BACKGROUND OF THE INVENTION

The ability to mold a deep recessed lip, or reverse lip, into a plasticarticle has traditionally been achieved through the use of injectionmolding. For example, in order to obtain a deep recessed reverse lip onthe rims of plastic containers, a manufacturer would inject, underpressure, molten plastic into an injection mold that defined the shapeof the lip and container. Injection molding is an expensive andcomplicated process, because it requires a very large initial capitaloutlay for equipment and molds.

SUMMARY OF THE INVENTION

The present invention differs significantly from the injection moldingmethod for forming a deep recessed lip in an article, in that itutilizes blow molding techniques. It provides the capability forproducing an article with a sturdy reverse lip while eliminating theexpense and complexity of injection molding.

The present invention is directed to an apparatus and method for blowmolding a recessed lip in a molded article. The apparatus comprises twoplates reciprocally movable toward and away from one another. A centermember is fixedly and perpendicularly mounted on each plate. A mold halfis mounted on each plate and is divided into two sections. One sectionis located on each side of the center ring member and is reciprocallymovable toward and away from the center member. A first member isassociated with each section in proximity to the center member and has achannel and a wall. A second member is reciprocally movable in thechannel and engages the center member. The recessed lip is moldedbetween the center member, the first member and the second member.

The method comprises the steps of providing a mold apparatus. The moldapparatus comprises a center member. A first member is located on eitherside of the center member includes a channel and a wall and isreciprocally movable toward and away from the center member. A secondmember is located in the channel and is reciprocally movable within thechannel. The second member slidably engages the center member. A parisonis extruded into the mold apparatus. The parison is sealed air tight inthe apparatus. The parison is pressurized and a portion of the parisonengages the center member and the second member. The first member ismoved toward the center ring. The recessed lip is formed against thecenter member, the first member and the second member. The parison isdepressurized and removed from the mold apparatus.

DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings a form which is presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

FIG. 1 is an isometric view of an article, prior to separation, whichmay be molded according to the present invention.

FIG. 2 is an isometric view of an article, after separation and showingthe recessed reverse lip, molded according to the present invention.

FIG. 3 is a sectional view taken along lines 3--3 in FIG. 2, showing theconfiguration of the recessed reverse lip.

FIGS. 4-9 are sectional views which illustrate the steps of the methodand the operation and interrelationship of the apparatus.

FIG. 10 is an isometric view of an alternate article which may be moldedaccording to the present invention.

FIG. 11 is an enlarged sectional view taken from FIG. 10, andillustrates a pair of reverse lips pinched together to form a rib.

DESCRIPTION OF THE INVENTION

Referring now to the drawings, wherein like numerals indicate likeelements, there is shown in FIG. 1 an article 10 which may be moldedaccording to the present invention. Illustrated article 10 is, forexample, two containers 12 and 12' which are simultaneously molded in asingle molding operation (discussed below). The two containers arejoined together at their respective recessed lips 14 and 14'. The twocontainers are separated, e.g. cut along a transverse planesubstantially through the middle of molded article 10, at the joinedlips 14, 14', such that containers 12 and 12' are of equal dimensionafter they are separated. FIG. 2 shows one of the two containers 12,after it has been separated. In FIG. 3, recessed lip 14 is shown incross section. The term "recessed lip" or "reversed lip" refers to agenerally U-shaped member which by its shape provides structuralstrength to the container. The lip may be, for example, 5/8"-1" indepth. An alternate article 8 made with the apparatus discussedhereinafter is illustrated in FIGS. 10 and 11. Article 8 is a drumhaving straight cylindrical walls and two ribs 9. One rib is illustratedin cross section in FIG. 11. Outwardly extending portions 9A of the ribare pinched together thereby sealing cavity 9B from the interior 8A ofthe drum. The seal prevents material from the inside of the drum fromaccumulating in cavity 9B. The rib adds strength to the drum andprevents the drum from bellying. The rib may also be used as a handle sothat the drum can be picked up and moved, e.g. by a fork lift truck.

Mold apparatus 16, shown in cross section in FIG. 4, is a threedimensional structure capable of molding articles ranging in size fromflower pots to garbage cans to 55 gallon drums. The specific moldapparatus shown in the figures produces a generally cylindrical flowerpot with tapered walls, a closed bottom and the reversed lip formedaround the opened top. The mold apparatus, however, is not limited tothat geometry. The mold apparatus is meant to cover any geometry inwhich one may wish to provide a reverse lip or a number of reverse lipsin a single article. One example of these geometries shown in FIGS. 1and 2. Another example, FIGS. 10 and 11, is a 55 gallon drum which iscylindrical with straight walls and has four circumferential reversedlips. The mold apparatus could be used to mold articles of any crosssection, by way of non limiting example, square, hexagonal, elliptical,triangular etc. Furthermore, the mold apparatus does not necessarilyhave to mold two containers, which are subsequently separated, singleoperation, instead a single article may be molded. Moreover, the top andbottom articles need not be symmetrical but can be different in size andshape. Accordingly, apparatus 16 should be envisioned as a block havinga mold cavity therein for molding any articles in which a reverse lip isdesired. The remaining discussion, however, will describe the apparatusand the process with regard to the article shown in FIG. 1.

Referring to FIG. 4, apparatus 16 comprises two horizontallyreciprocally movable mold halves, left mold half 22 and right mold half24, which are arranged symmetrically around a plane Y--Y. Mold half 22is a mirror image of mold half 24. Each mold half is horizontallydivided, by a plane X--X, into two vertically reciprocally movablesections. Mold half 22 comprises sections I and III, and mold half 24comprises sections II and IV. When closed together, these sectionsdefine the shape of the article to be molded. Moving the sections apartallows the article to be released after it has been molded. The X--X andY--Y planes divide apparatus 16 along its horizontal and vertical axis,respectively.

Only mold half 22 will be described in detail, as those skilled in theart will understand that the description applies equally well to moldhalf 24. A plate 18 is capable of horizontal reciprocal movement alongplane X--X toward and away from its mirror image 18', but it is notvertically movable along the plane Y--Y. Center ring member 20 isaffixed to plate 18 preferably equidistant from its ends. Center ringmember 20 is arranged perpendicular to plate 18, that is, along X--X asviewed in FIG. 4. Surface 20A of ring member 20 is semicircular in thehorizontal or X--X plane, so that when in contact with its mirror image20', they define, in combination, a generally circular surface. Ofcourse, if the mold apparatus is used to mold an article of square crosssection, the surface 20A would have to define one half of the squaresurface.

Sections I and III of mold 22 are slidably mounted upon plate 18 vialinear thrust bearings 26 for reciprocal movement in the vertical orY--Y plane toward and away from center ring member 20. Sections I andIII are arranged symmetrically around plane X--X and are disposed oneither side of center ring member 20 as shown in FIG. 4. Section I ismirror image of section III except as noted below, and therefore onlysection I will be described in detail.

A mobile plate 27, having a surface 27A, rides on bearings 26. Mobileplate 27 is capable of reciprocal movement toward and away from ringmember 20. Mold wall 28 is rigidly affixed to plate 27 along surface27B. Plate 27 can be eliminated in which case mold wall 28 would beslidably mounted on the bearings. Surface 28A of mold wall 28 defines asubstantially hemicylindrical but slightly tapered volume, so that whenwall 28 is in contact with its mirror image 28', they define, incombination, a generally cylindrical but tapered volume. Of course, if ashape other than that described is desired, wall 28 would have to definethat shape.

Pinch off plate 30 is movably affixed on an upper surface 28B of moldwall 28. Pinch off plate 30 is reciprocally movable, along thehorizontal, or X--X plane, with respect to mold wall 28, toward and awayfrom its mirror image 30' of section II. Pinch off plate 30 issubstantially rectangular and has a hemicylindrical bore 32 along itsinner surface 34 and includes pinch off edge 32A. The bore 32 in pinchoff plate 30 cooperates with its mirror image bore 32' in the pinch offplate 30' to form a cylindrical bore which provides clearance forplastic flash from the parison and a blow tube 36 used in the moldingprocess. Blow tube 36 can be eliminated as can the cylindrical bore, ifknown parison puncturing blow needles are used. Plates 30 and 30' aremovable between a first position and a second position. In the firstposition (see FIG. 4) plates 30 and 30' are completely extended, i.e.spaced away from plates 27 and 27' respectively. When mold halves 22 and24 are moved together (see FIG. 5) the mating pinch off edges 32A, 32A'form a tight seal about blow tube 36. (see the upper portion of thedrawing in FIG. 5). In the second position (see FIG. 8), plates 30, 30'are in a completely retracted position, i.e. abutting plates 27 and 27'respectively.

Lower pinch off plates, 38, 38' of sections III, IV, respectively, donot require the bore 32 to provide clearance for blow tube 36. Pinch offplates 38, 38' instead comprise pinch off edges 40A and 40A',respectively. In addition, clearances 40 and 40' cooperate to provideclearance space for any excess portion of plastic which is extrudedduring the molding process. Lower pinch off plates 38 and 38' aremovable between a first position and a second position. In the firstposition (see FIG. 4) plates 38 and 38' are completely extended, i.e.spaced away from plates 27 and 27' respectively. When mold halves 22 and24 are moved together (see FIG. 5) the mating pinch off edges 40A, 40A'form a tight seal at the base of the mold. Any excess plastic is caughtbetween clearances 40 and 40'. In the second position (see FIG. 8),plates 30, 30' are in a completely retracted position, i.e. abuttingplates 27 and 27' respectively.

Mold walls 28, 28' and pinch off plates 30, 30' together define a frustoconical cavity 42 which, when brought together, defines the shape 12A ofarticle 10. Of course, if a different shape is desired, the shape of thecavity must correspond to the desired shape.

First insert ring member 44 is affixed to wall 28 in a recess 28C in theproximity of center ring member 20. First insert ring member 44 may beformed as part of wall 28, instead of the discrete member illustrated. Awall 44A of first ring member 44 cooperates with mold wall 28 to definea second frusto conical cavity portion 46 which, when brought together,defines a circumferential shoulder 12B for the finished article 10.First insert ring member 44 is also provided with a channel 47 (see FIG.6) into which is placed second insert ring member 48. First insert ringmember 44 is preferably made of steel, but any metal with propertiessimilar to those of steel will suffice.

Second insert ring member 48 is vertically reciprocally movable, i.e. inthe Y--Y plane, within the channel 47 and is biased away from theinterior of the channel by coil springs 50 (only one shown). Secondinsert ring member 48 is preferably made of bronze, but any metal havingproperties similar to those of bronze will suffice.

Second insert ring member 48 is L-shaped in cross section and isreciprocally slidable between a first position and a second position.Second insert ring member 48 has a shoulder 52 which slidably engagessurface 20A of ring member 20. Spring 50 biases ring member 48 to thefirst position (see FIG. 4), i.e. out of channel 47, in which theshoulder 52 of ring member 48 bears against surface 20A. Spring 50maintains second insert ring 48 at its first position until movement ofmold section (note arrow B of FIG. 6) cause engagement of a surface 48Awith center ring member 20. Since spring 50 maintains member 48 in itsfirst position until engagement with ring member 20, parison 54 whichengages concave surface 48B forms wrinkle 56. Spring 50 yields toforces, discussed below, applied against a surface 48A by center ring 20(see FIG. 6) and allows ring member 48 to move to the second position(see FIG. 7) in which base 48C of ring member 48 abuts the bottom ofchannel 47.

Referring to FIGS. 4-9 in sequence, the operation of mold apparatus 16will be described. Referring to FIG. 4, mold apparatus 16 is illustratedin its initial position. Upper mold sections I and II are separated fromlower mold sections III and IV. In addition mold halves 22 and 24 areseparated from each other. A parison 54, or a tube of plastic from anextruder (not shown), is extruded around blow tube 36, and between themold halves 22, 24 of mold apparatus 16. The parison 54 may bepolyethylene, however any thermoplastic which is blow moldable may beused. A polyethylene parison is typically extruded at a temperature ofabout 375° F. The temperatures and pressures set forth herein describethe process when polyethylene is blow molded. Temperatures and pressuressuitable for other blow moldable thermoplastics are conventional andwithin the ordinary skill in the art.

Referring to FIG. 5, the right and left mold halves, 22, 24 of moldapparatus 16 are moved together in the direction indicated by arrows A.Pinch off edges 32A, 32A' and 40A, 40A' seal the parison air tight andprepare the flash 54A of the parison 54 for easy removal. The section ofparison 54 which is inside the mold 16 is then inflated or pressurizedwith air between about 60 and 150 psi so that the parison 54 is expandedand formed on the inner surface of the mold cavity. A portion 58 of theparison 54 is pushed out of the interior of the mold cavity and engagessurfaces 20A and 48B. Thereafter the air pressure in the mold cavity maybe lowered to about 5 to 40 psi. This depressurization of the parison isoptional.

Referring to FIG. 6, which shows the right mold half 24, top moldsection II and the bottom mold section IV are moved together in thedirection indicated by the arrows B. As the mold sections are pushedtogether portion 58 is compressed in the direction shown by arrows B'and forms a wrinkle 56 because spring 50 will not yield to forcescreated by portion 58 against surface 48B. Further movement of the moldsections in the direction of arrows B forces surface 48A of secondinsert ring member 48 to engage ring member 20. Ring member 48 thenmoves into its second position and in doing so compresses spring 50.This movement causes portion 58 to slide against surface 20A and formagainst the curved surface 48B. If the article is not to separatedacross the upper and lower halves of the reversed lip (for example toform rib 9), walls 44A should be sufficiently tall so that when ringmember 48 reaches its second position the parison there between is incontact and sealed or pinched together. When this is done, it may benecessary to puncture the reverse lip, with needles, to allow the escapeof air pressure (not shown) and avoid explosion of rib 9.

Mold sections II and IV continue moving in the direction indicated byarrows B until they are brought into full contact with ring member 20',see FIG. 7. The compression of second insert ring member 48 into channel47 has made room for the portion 58 which has expanded in the directionshown by arrows C. Wrinkle 56, shown in phantom, has disappeared. Atthis time, air pressure of approximately 60 to 150 psi is returned, ifthe parison was previously depressurized, to the inside of the moldcavity and parison 54, to reform the part and speed the cooling process.The entire series of movements of the various mold sections describedabove happens rapidly, i.e. in less than 2 seconds.

Referring to FIGS. 8 and 9, the parison 54 is depressurized and plates30, 30' and 38, 38' are retracted in the direction indicated by arrows Dinto their second position, abutting plates 27, 27'. The mold sectionsare then separated as shown by arrows E and article 10 is removedtherefrom.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof and,accordingly, reference should be made to the appended claims, ratherthan to the foregoing specifications, as indicating the scope of theinvention.

We claim:
 1. An article produced by a method of blow molding a deeprecessed portion onto a molded part comprising the steps of: providing amold apparatus with two mold sections, each mold section comprising acenter member, a first member on either side of said center member, saidfirst members being reciprocally movable toward and away from saidcenter member and having a channel therein and a wall, and a secondmember reciprocally movable within each said channel and biased towardand slidably engaging said center member; extruding a parison into saidmold apparatus; closing said mold sections and sealing said parison airtight in said apparatus; pressurizing said parison in said apparatus andthereby forcing a portion of said parison into engagement with saidcenter member and said second members, moving each said first memberwith said second number therein toward said center member to form ahollow body having at least one hollow recessed portion formed by themovement of the center member and the first and second members;depressurizing said hollow body; moving said mold sections away from oneanother; removing said hollow body from said mold apparatus, whereinsaid hollow body has at least one recessed portion which is symmetricwith respect to a transverse plane through said hollow body; andsectioning the hollow body along said recessed portion so as to dividethe hollow body into two pieces, each piece of the hollow body forming asaid article and including at least part of said recessed portion suchthat each piece has a U-shaped cross-sectional portion spaced from saidside wall and an outwardly extending flange portion projecting from saidside wall where the hollow body was divided; said outwardly extendingportion traversing the space between and joining said side wall to theU-shaped portion.
 2. An article made using a blow molding processcomprising: a bottom having a center axis; at least one side wallforming a symmetrical hollow body with respect to the center axis ofsaid bottom; an open top; a recessed portion substantially U-shaped incross-section formed around an outer periphery of the open top andspaced from said side wall, said recessed portion joined to said opentop of said side wall by an outwardly extending web portion whichprojects from said outer periphery, the recessed portion forming amechanical strengthening member for said article.
 3. An articleaccording to claim 2, wherein said article is made of a plasticmaterial.